Ozone gas sensing element, detection apparatus, and measurement method

ABSTRACT

A sensing element in which a dye that changes in the light absorption characteristic of the visible region upon reaction with ozone gas is deposited in the pores of a porous material is prepared. A change in dye before and after exposing the sensing element to a measurement environment for a predetermined time is measured. The ozone gas amount in measurement target air is measured on the basis of the change in dye.

BACKGROUND OF THE INVENTION

The present invention relates to an ozone gas sensing element, detectionapparatus, and measurement method.

At present, air pollution by NO, SPM, and photochemical oxidant occurs,and the influence on the environment is serious. Ozone as a maincomponent of photochemical oxidant is produced by photochemical reactionof a pollutant such as NO_(x) or hydrocarbon emitted by factories,business offices, and vehicles upon irradiation with sunlight, andcauses a photochemical smog.

In Japan, air quality standards have been set for, e.g., thephotochemical oxidant concentrations of these substances in air. The gasconcentration is measured using analytical instruments that utilizeultraviolet absorption in general air monitoring stations at manyplaces. The air quality standard is an average of 60 ppb or less perhour.

In gas concentration measurement using analytical instruments, a smallamount of gas at several ppb can be measured. However, this instrumentis expensive and requires maintenance. Analytical instrument requiresvery high power cost, apparatus maintenance cost, and the like. Inaddition, many restrictions are posed such that a power supply, astandard gas for calibration, and humidity-controlled dedicated roommust be ensured.

In order to perform investigation of the gas concentration distributionand evaluation of the influence on the terrestrial environment at highprecision, the number of monitoring points must be increased to monitorthe environment on a nationwide scale. For this purpose, a demand hasarisen for cumulative use of low-cost, compact, and easy-to-use gassensors or passive measurement methods (or monitoring apparatuses).

To meet this demand, a semiconductor gas sensor, solid electrolyte gassensor, electrochemical gas sensor, quartz crystal oscillation gassensor, and the like are widely developed. However, these gas sensorsare developed for evaluating a response within a short time, and not formonitoring which requires data accumulation. If accumulation isnecessary, the gas sensor must always be operated. The detection limitis sub-ppm (1 ppm or less), and the gas sensor cannot cope with thedetection of ozone at the concentration (e.g., about 10 ppb for ozone)in an actual environment. The influence of another gas cannot be ignoredin many cases.

Also, a method using a passive sampler is developed forlong-term-averaged measurement on the spot, and is not proper forcumulative use. This method suffers problems such that an operator mustgo to the site and an individual difference occurs in reading color. Theinterference or disturbance of another gas often poses a problem.

As the passive measurement method, ozone is sampled by a suction pumpinto a glass bottle cleaned with purified water so as not to mix air.Ozone in water is absorbed in a potassium iodide solution to titrateprecipitated iodine. This method requires not only a sample, but alsoperipheral devices such as a pump and pH adjustment immediately afterwater sampling. Further, detection processing must be executed.

Conventional gas concentration measurement requires an expensive, bulkyapparatus arrangement in order to detect ozone gas at high precision inppb order in accordance with the air quality standard. Measurement iscumbersome, and ozone gas cannot be easily detected.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an ozone gas sensingelement, detection apparatus (measurement apparatus), and detectionmethod (measurement method) capable of detecting ozone gas more easilyat higher precision than the prior art.

It is another object of the present invention to provide an ozone gassensing element, detection apparatus (measurement apparatus), anddetection method (measurement method) capable of cumulative use.

It is still another object of the present invention to provide an ozonegas sensing element, detection apparatus (measurement apparatus), anddetection method (measurement method) in which interference ordisturbance of another gas is negligible.

To achieve the above objects, an ozone gas measurement method accordingto the present invention comprises the steps of preparing a sensingelement in which a dye (stain) that changes in a light absorptioncharacteristic of a visible region upon reaction with ozone gas isdeposited in a pore of a porous material, exposing the sensing elementto a measurement environment for a predetermined time, and measuring anozone gas amount in a target gas on the basis of a change in the lightabsorption before and after exposing the sensing element to themeasurement environment for a predetermined time.

An ozone gas sensing element according to the present inventioncomprises a porous material, and a dye (stain) which is deposited in apore of the porous material and changes in a light absorptioncharacteristic of a visible region upon reaction with ozone gas.

An ozone gas measurement apparatus according to the present inventioncomprises a light-emitting unit, a light-detecting unit, a sensingelement, and a signal processing unit, wherein the light-emitting unitemits light having a predetermined wavelength, the sensing element isinterposed between the light-emitting unit and the light-detecting unit,and comprises a porous material, and a dye which is deposited in a poreof the porous material and changes in a light absorption characteristicof a visible region upon reaction with ozone gas, the light-detectingunit comprises a light-receiving surface arranged to face thelight-emitting unit, receives, via the sensing element, light emitted bythe light-emitting unit, and outputs a signal corresponding to a lightquantity received by the light-receiving surface, and the signalprocessing unit calculates an ozone gas amount on the basis of thesignal output from the light-detecting unit and a light absorptioncharacteristic, obtained in advance, of the sensing element whichcontains the dye before reaction with the ozone gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1C are views for explaining a method of manufacturing anozone gas sensing element according to an embodiment of the presentinvention;

FIGS. 1D to 1F are views for explaining an ozone gas detection methodaccording to the embodiment of the present invention;

FIG. 2 is a graph showing the results of two absorbance measurementsaccording to the embodiment of the present invention;

FIG. 3 is a schematic view showing the arrangement of a sensing elementaccording to the embodiment of the present invention;

FIG. 4 is a correlation diagram showing the relationship between theozone concentration and the transmittance in a sensing element accordingto the first embodiment;

FIG. 5 is a correlation diagram showing the relationship between a glassporous material and the light transmittance;

FIG. 6 is a graph showing the characteristic of a sensing elementaccording to the second embodiment of the present invention;

FIG. 7 is a graph showing the results of two absorbance measurements inan ozone gas detection method according to the second embodiment of thepresent invention;

FIG. 8 is a graph showing the results of two absorbance measurements inan ozone gas detection method according to the third embodiment of thepresent invention;

FIG. 9 is a graph showing the results of two absorbance measurements inan ozone gas detection method according to the fourth embodiment of thepresent invention;

FIG. 10 is a graph showing the results of two absorbance measurements inanother ozone gas detection method according to the fourth embodiment ofthe present invention;

FIG. 11 is a graph showing the results of two absorbance measurements inan ozone gas detection method according to the fifth embodiment of thepresent invention;

FIG. 12 is a graph showing the results of two absorbance measurements inan ozone gas detection method according to the sixth embodiment of thepresent invention;

FIG. 13 is a graph showing the results of two absorbance measurements inan ozone gas detection method according to the seventh embodiment of thepresent invention;

FIG. 14 is a graph showing the results of two absorbance measurements inan ozone gas detection method according to the eighth embodiment of thepresent invention; and

FIG. 15 is a block diagram showing the schematic arrangement of an ozonegas detection apparatus according to an embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the accompanying drawings.

First Embodiment

An ozone gas detection method (measurement method) according to thefirst embodiment will be explained.

A sensing element fabrication method will be described.

As shown in FIG. 1A, a mixture solution 101 containing Orange I ethanolsolution and water is prepared in a vessel 102. The Orange Iconcentration is 0.2%.

As shown in FIG. 1B, a porous material 103 is immersed in the solution101. An example of the porous material 103 is porous glass having anaverage pore diameter of 4 nm. The first embodiment adopts Vycor 7930available from Corning as the porous material 103. The size of theporous material is a chip size of 8 (mm)×8 (mm) with a thickness of 1(mm).

The porous material 103 is immersed in the solution 101 for 24 hrs toimpregnate the pores of the porous material 103 with the solution. Afterthat, the porous material 103 is air-dried. As shown in FIG. 1C, theporous material 103 is left dried in a nitrogen gas flow for 24 hrs ormore, thereby fabricating a sensing element 103 a.

An ozone gas detection method (measurement method) using the sensingelement 103 a will be described.

As shown in FIG. 1D, the absorbance of the sensing element 103 a in thedirection of thickness is measured. In FIG. 1D, I₀ represents the lightintensity of an incident light, and I represents the intensity oftransmitted light. In this case, the absorbance is given by log₁₀(I₀/I).

As shown in FIG. 1E, the sensing element 103 a is exposed for apredetermined time, e.g., 3 hrs to detection target air 104 containingozone at a concentration of, e.g., 100 ppb. Thereafter, the sensingelement 103 a is extracted from the detection target air 104. As shownin FIG. 1F, the absorbance of the sensing element 103 a in the directionof thickness is measured again.

FIG. 2 shows the results of two absorbance measurements (absorbanceanalyses). In measurement, no absorbance is measured at a transmittedlight measurement wavelength of 350 nm or less because light is absorbedby porous glass (Vycor 7930) which constitutes the sensing element.

In FIG. 2, the broken line represents the measurement result of theabsorbance before exposure to detection target air, and the solid linerepresents the measurement result of the absorbance after exposure todetection target air. Both the solid and broken lines exhibit absorptionof water around wavelengths of 1,350 nm and 1,900 nm. Absorption changesaround wavelengths of 1,350 nm and 1,900 nm depending on the humidity ofdetection target air and the standing time of the sensing element.Hence, the effective measurement wavelength range of the ozone gasdetection method (measurement method) using the sensing element 103 a isdetermined to be 350 nm to 1,000 nm.

A large difference is found between the solid and broken lines in awavelength range of 400 nm to 600 nm, particularly around 480 nm.Measurement of the absorbance after the sensing element 103 a is exposedto detection target air exhibits a decrease in absorption at awavelength of 480 nm. This means that, when the sensing element 103 a isexposed to detection target air, the dye (stain) in the sensing elementis decomposed to produce a new decomposition product. This product canbe estimated to be produced by decomposing a diazo group contained inthe molecular skeleton of Orange I.

In the first embodiment, ozone gas is detected by measuring a change indye (stain) color before and after reaction with ozone.

The sensing element according to the first embodiment will be explained.

As shown in FIG. 3, a sensing element 302 fabricated by theabove-described manufacturing method has a transparent matrix shapehaving a plurality of pores 301 with an average pore diameter of, e.g.,20 nm or less. The sensing element 302 functions as an adsorbent. Atleast some pores 301 in a porous material 305 are coupled to pores onthe surface of the porous material.

The dye (stain) is deposited in the pore 301 of the sensing element 302.The porous material is exposed to air, and then moisture in air isadsorbed in the pore to form a thin water film. As a result, a thin film303 of an aqueous solution (trapping and detective solution) in whichthe dye (stain) is dissolved can be estimated to be formed on the innerwall of the pore 301 of the sensing element 302. At least some pores 301are coupled to pores on the surface of the porous material, so the dyecan be estimated to be deposited in at least some pores.

An ozone molecule 304 which enters the pore. 301 of the sensing element302 reacts with the dye to decompose a diazo group. That is, theπ-electron system extending over the molecule is split into two. Thesplit molecule does not absorb any light around 480 nm, and the color ofthe sensing element 302 fades. That is, the dye causes fading reactionwith ozone. At least some pores 301 are coupled to pores on the surfaceof the porous material, and ozone gas is estimated to react with the dyedeposited in at least some pores.

A decomposed molecule can, therefore, be quantitatively measured bymeasuring the absorption spectrum of the sensing element by, e.g., aspectrophotometer (absorptiometer). By quantitative measurement, ozonegas can be indirectly measured.

For example, a porous material is made of a material which transmitslight in the light absorption wavelength range of the dye. The lightabsorption characteristic of the sensing element which adsorbs ozone gasis measured. By measuring the light absorption characteristic, theadsorbed ozone gas can be detected.

As described above, the first embodiment executes measurement when thesensing element is exposed for 3 hrs to detection target air at an ozoneconcentration of 100 ppb. As a result of absorbance measurement, asshown in FIG. 2, a change in absorbance at a wavelength of 480 nm is aslarge as about 0.17, and ozone gas can be detected at high-sensitivity100 ppb level.

The absorbance is measured by fixing the sensing element 103 a to thethin film measurement holder of the absorptiometer. Quantitativemeasurement at ppb level can be achieved by obtaining the relationshipbetween the difference in absorbance and the concentration frommeasurement of the absorbance.

A change in absorbance at the maximum absorption wavelength per exposureamount (concentration (ppb)×exposure time (h)) is obtained as thesensitivity index. In the first embodiment, as shown in FIG. 2, a changein absorbance after exposure to 100-ppb ozone gas for 3 hrs is 0.17. Thesensitivity index is 5.7×10⁻⁴ ppb⁻¹·hr⁻¹, and very high sensitivity canbe attained.

As described above, the first embodiment prepares a sensing element inwhich a dye that irreversibly changes in the absorbance of the visibleregion upon reaction with ozone gas is deposited in the pores of atransparent porous material. It is estimated that, when the sensingelement is exposed to an ozone gas-containing atmosphere, a double bondsuch as a diazo group in the dye is broken by ozone gas adsorbed in thepores of the sensing element, and the electron state of the dye moleculechanges to change the absorption spectrum of the visible region. Hence,ozone gas can be detected when the color of the sensing element changesand the first and second transmittances become different.

The first embodiment has exemplified the use of Orange I as a dye.Examples of a diazo dye are Orange II, Orange G, Methyl Orange, BismarckBrown, Methyl Yellow, Acid Chrome Violet K, Crocein Orange G,Chromotrope FB, New Coccine, Crystal Scarlet, Alizarin Blue Black R,Plasmocorinth B, Sudan II, Sudan III, Sudan IV, Sudan Red B. Sudan Red7B, Sunset Yellow FCF, Toluidine Red, Tropaeoline O, Xylidine Ponceau2R, zincon monosodium salt, Benzopurpurin 4B, Biebrich Scarlet Red,Bordeaux R, Brilliant Crocein MOO, 2-(5-bromo-2-pyridylazo)5-(diethylamino) phenol, 6′-butoxy-2,6-diamino-3,3′-azodipyridine, AcidBlack 24, Acid Blue 29, Acid Blue 92, Acid Blue 113, Acid Blue 120, AcidOrange 8, Acid Orange 51, Acid Orange 63, Acid Orange 74, Acid Red 1,Acid Red 4, Acid Red 8, Acid Red 37, Acid Red 97, Acid Red 114, Acid Red151, Acid Red 183, Acid Violet 7, Acid Yellow 17, Acid Yellow 25, AcidYellow 29, Acid Yellow 34, Acid Yellow 42, Acid Yellow 76, Acid Yellow99, Alizarin Yellow GG, Allura Red AC, Amaranth, Calcion, Chicago SkyBlue 6B, Chromotrope 2B, Chromotrope 2R, chrysoidin, Congo Red, DirectBlue 71, Direct Red 23, Direct Red 75, Direct Red 80, Direct Red 81,Direct Violet 51, Direct Yellow 50, Direct Yellow 62, Disperse Red 1,Disperse Red 19, Disperse Yellow 3, Eriochrome Blue Black B, EriochromeBlack T, Evans Blue, Fat Brown RR, Metanil Yellow, Naphthol Blue Black,Nitrazine Yellow, Nitro Red, Nitrosulfonazo III, Solvent Red 26, and OilRed O. An example of a dye is a triphenylmethane stain (e.g., MalachiteGreen, Crystal Violet, or fuchsine). An example of a dye is an indigoidstain containing indigo (e.g., indigo or indigo -carmine).

An example of a dye is a dye which is an aromatic compound (e.g.,benzene, naphthalene, or anthracene) and has a diazo group. By usingthese dyes, ozone can be specifically detected even in the presence ofanother gas.

An example of a dye is a diazo dye which is an aromatic compound (e.g.,benzene, naphthalene, or anthracene) and has a hydroxyl group, asulfurous acid group, or primary to tertiary amino groups. By usingthese dyes, ozone can be specifically detected even in the presence ofanother gas. In addition, the stability of the dye can be obtained tomore stably detect ozone.

As a method of introducing a dye into the pores of a porous material,the porous material is impregnated with the dye by using a solution, andthe dye is introduced into pores and dried. As another method, the dyemay be introduced into pores by vapor deposition. As still anothermethod, the dye may be mixed with another compound and introduced intopores in fabricating a porous material by the sol-get method.

According to the first embodiment, the adsorption area of ozone gas tobe detected can be increased by using the sensing element 103 acontaining the dye in the pores of the porous material. Compared to aconventional method, the sensitivity and accumulation capacity can beincreased, realizing cumulative use.

According to the first embodiment, the porous material which constitutesthe sensing element 103 a has a high transmittance in a wavelengthregion of about 350 nm to 1,000 nm. A change in the absorbance of thesensing element which is decomposed upon adsorption of ozone in thesensing element can be measured by measuring the transmittance of thesensing element. That is, absorbances of the sensing element before andafter exposing the sensing element 103 a to detection target air aremeasured and compared. As a result, ozone gas adsorbed in the sensingelement 103 a can be detected to easily detect ozone gas. In absorbancemeasurement, only a change in single peak suffices to be monitored, andmeasurement is easy.

In the sensing element according to the first embodiment, the lighttransmittance of the sensing element at a predetermined wavelengthincreases as the ozone gas concentration in measurement target airincreases. The predetermined wavelength is about 480 nm in the case ofthe first embodiment.

The first embodiment can detect ozone gas from an optical change byusing the compact sensing element 103 a, and can very easily detectozone gas at high precision.

As for the relationship between the porous material which constitutesthe sensing element and its light transmittance, as shown in FIG. 5,when the sensing element is made of porous glass (borosilicate glass),light passes in the visible light region (350 nm to 800 nm) inmeasurement of the transmission spectrum in the UV visible wavelengthregion (wavelength: 200 nm to 2,000 nm) by setting the average porediameter to 20 nm or less. For a larger average pore diameter, an abruptdecrease in transmittance in the visible region is observed.

In FIG. 5, the dotted line represents the transmittance of silica glass;the chain line, the transmittance of a borosilicate glass porousmaterial having a pore diameter of 2.5 nm; the solid line, thetransmittance of Vycor 7930 adopted in the first embodiment; and thebroken line, the transmittance of a borosilicate glass porous materialhaving a pore diameter of 20 nm.

Samples represented by the chain and broken lines are available fromGeltec. The thicknesses of all samples used in the transmittancemeasurement method are 1 mm.

From the results shown in FIG. 5, the porous material preferably has anaverage pore diameter of 20 nm or less. The size of the dye is estimatedto be 0.3 nm to 5 nm, and can be deposited in the pores of the porousmaterial. A transparent porous material is preferably used in a visiblerange of 350 nm to 800 nm. In the first embodiment, the specific surfaceof the porous material is 100 m² or more per g.

Second Embodiment

An ozone gas sensing element according to the second embodiment of thepresent invention will be described.

An ozone gas sensing element fabrication method according to the secondembodiment will be explained.

As shown in FIG. 1A, a solution obtained by dissolving sodium carbonatein water is prepared as an alkali solution. The sodium carbonateconcentration is 5%.

As shown in FIG. 1B, a porous material having an average pore diameterof 4 nm is dipped in the alkali solution for a predetermined time, e.g.,2 hrs, and then cleaned with pure water.

This porous material is identical to that described in the firstembodiment, and is made of Vycor 7930 available from Corning. The porousmaterial has a chip size of 8 (mm)×8 (mm) with a thickness of 1 (mm).

A solution is prepared by dissolving fuchsine in ethanol. The fuchsineconcentration is 0.002%. The porous material which has been dipped inthe alkali solution and cleaned with pure water is immersed in thefuchsine ethanol solution for 2 hrs to impregnate the solution into thepores of the porous material. Thereafter, the porous material isair-dried, and left dried in a nitrogen gas flow for half a day or more.Consequently, a sensing element according to the second embodiment isfabricated.

In the above-described fabrication method, a comparative sensing elementis fabricated by dipping a porous material in pure water instead of analkali solution and then in a fuchsine solution. The absorbances of thesensing element according to the second embodiment and the comparativesensing element fabricated in the above manner are measured.

A change in absorbance at 545 nm upon when the sensing element accordingto the second embodiment and the comparative sensing element are left tostand in nitrogen gas will be explained with reference to FIG. 6.

The absorbance of the comparative sensing element which does not undergoalkali treatment changes even in nitrogen. To the contrary, theabsorbance of the sensing element according to the second embodimentwhich undergoes alkali treatment is stable without any change.

A change in absorption spectrum before and after exposing, tomeasurement target air, the sensing element according to the secondembodiment that has undergone alkali treatment will be described withreference to FIG. 7. In FIG. 7, the broken line represents theabsorption spectrum before exposing the sensing element of the secondembodiment to air. The solid line represents the absorption spectrumafter exposing the sensing element of the second embodiment for 24 hrsto air containing ozone gas at a concentration of 100 ppb.

In FIG. 7, the sensing element of the second embodiment represented bythe solid line exhibits a decrease in absorption at a wavelength of 545nm. This is estimated to occur because fuchsonimine in the fuchsinemolecule is decomposed by ozone, i.e., the π-electron system is split.

The absorbance change is as large as about 0.1, and ozone gas can bedetected at high-sensitivity ppb level even by ozone gas detection usingthe sensing element of the second embodiment.

Referring to FIG. 7, the sensitivity index is obtained to be 4.2×10⁻⁵ppb⁻¹·hr⁻¹, and very high sensitivity can be attained.

As described above, the second embodiment prepares a sensing element inwhich a mixture of alkali and a dye (stain) that changes in theabsorbance of the visible region upon reaction with ozone gas isdeposited in the pores of a transparent porous material. It is estimatedthat, when the sensing element is exposed to an ozone gas-containingatmosphere, a double bond such as C═C in the dye is broken by ozone gasadsorbed in the pores of the sensing element, and the electron state ofthe dye molecule changes to change the absorption spectrum of thevisible region. Ozone gas can, therefore, be detected when the color ofthe sensing element changes and the first and second transmittancesbecome different.

The second embodiment has exemplified the use of fuchsine as a dye. Anexample of a dye is a triphenylmethane stain (e.g., Malachite Green orCrystal Violet).

As a method of introducing a dye into the pores of a porous material,the porous material is impregnated with the dye by using a trapping anddetective solution, and the dye is introduced into pores and dried. Asanother method, the dye may be introduced into pores by vapordeposition. As still another method, the dye may be mixed with anothercompound and introduced into pores in fabricating a porous material bythe sol-get method.

According to the second embodiment, the adsorption area of ozone gas tobe detected can be increased by using a sensing element 103 a containingthe dye in the pores of the porous material. Compared to a conventionalmethod, the sensitivity and accumulation capacity can be increased,realizing cumulative use.

The second embodiment has exemplified the use of an aqueous solutionprepared by dissolving sodium carbonate in water as an alkali solution.Examples of alkali are an alkali itself and alkali salt. A desirableexample of an alkali salt is a salt of a weak acid and a strong alkali.

Also in the second embodiment, the porous material preferably has anaverage pore diameter of 20 nm or less.

Third Embodiment

An ozone gas sensing element according to the third embodiment of thepresent invention will be described.

An ozone gas sensing element fabrication method according to the thirdembodiment will be explained.

As shown in FIG. 1A, a solution is prepared by dissolving, in water,Methyl Orange as a dye (stain) and triethanolamine as an acid gassorbent. The Methyl Orange concentration is 0.35%, and thetriethanolamine concentration is 1.0%.

As shown in FIG. 1B, a porous material having an average pore diameterof 4 nm is immersed in the solution. The porous material is identical tothat described in the first embodiment, and is made of Vycor 7930available from Corning. The porous material has a chip size of 8 (mm)×8(mm) with a thickness of 1 (mm).

The porous material is immersed in the solution for 2 hrs to impregnatethe pores of the porous material with the solution. The porous materialis air-dried, and left dried in a nitrogen gas flow for half a day,thereby fabricating a sensing element according to the third embodiment.

Absorption spectra before and after exposing the sensing element of thethird embodiment to measurement target air will be described withreference to FIG. 8. In FIG. 8, the broken line represents theabsorption spectrum before exposure to measurement target air. The solidline represents the absorption spectrum after the sensing element of thethird embodiment is exposed for 24 hrs to air containing ozone gas at aconcentration of 100 ppb.

As shown in FIG. 8, the sensing element of the third embodiment exhibitsa decrease in absorption around a wavelength of 510 nm. This decrease isabout 0.3, and ozone gas can be detected at high-sensitivity ppb level.

Referring to FIG. 8, the sensitivity index is obtained to be 1.3×10⁻⁴ppb⁻¹·hr⁻¹.

In the above-described fabrication method, a comparative sensing elementwas fabricated except triethanolamine. The influence of disturbance ofNO₂ as an acid gas was investigated using the comparative sensingelement. As a result, the comparative sensing element observeddisturbance of NO₂, but the sensing element of the third embodiment didnot observe any disturbance of NO₂.

As described above, the third embodiment prepares a sensing element inwhich a mixture of an acid gas sorbent and a dye (stain) that changes inthe absorbance of the visible region upon reaction with ozone gas isdeposited in the pores of a transparent porous material. It is estimatedthat, when the sensing element is exposed to an atmosphere containingozone gas and many acid gases other than ozone gas, a double bond suchas N═N in the dye is broken by ozone gas adsorbed in the pores of thesensing element almost free from disturbance of an acid gas, and theelectron state of the dye molecule changes to change the absorptionspectrum of the visible region. Ozone gas can, therefore, be detectedwhen the color of the sensing element changes and the first and secondtransmittances become different.

The third embodiment has exemplified the use of Methyl Orange as a dye.Examples of a dye are Orange I, Orange II, Orange G, Bismarck Brown,Methyl Yellow, Acid Chrome Violet K, Crocein Orange G, Chromotrope FB,New Coccine, Crystal Scarlet, Alizarin Blue Black R, Plasmocorinth B,Sudan II, Sudan III, Sudan IV, Sudan Red B, Sudan Red 7B, Sunset YellowFCF, Toluidine Red, Tropaeoline O, Xylidine Ponceau 2R, zinconmonosodium salt, Benzopurpurin 4B, Biebrich Scarlet Red, Bordeaux R,Brilliant Crocein MOO, 2-(5-bromo-2-pyridylazo) 5-(diethylamino) phenol,6′-butoxy-2,6-diamino-3,3′-azodipyridine, Acid Black 24, Acid Blue 29,Acid Blue 92, Acid Blue 113, Acid Blue 120, Acid Orange 8, Acid Orange51, Acid Orange 63, Acid Orange 74, Acid Red 1, Acid Red 4, Acid Red 8,Acid Red 37, Acid Red 97, Acid Red 114, Acid Red 151, Acid Red 183, AcidViolet 7, Acid Yellow 17, Acid Yellow 25, Acid Yellow 29, Acid Yellow34, Acid Yellow 42, Acid Yellow 76, Acid Yellow 99, Alizarin Yellow GG,Allura Red AC, Amaranth, Calcion, Chicago Sky Blue 6B, Chromotrope 2B,Chromotrope 2R, chrysoidin, Congo Red, Direct Blue 71, Direct Red 23,Direct Red 75, Direct Red 80, Direct Red 81, Direct Violet 51, DirectYellow 50, Direct Yellow 62, Disperse Red 1, Disperse Red 19, DisperseYellow 3, Eriochrome Blue Black B, Eriochrome Black T, Evans Blue, FatBrown RR, Metanil Yellow, Naphthol Blue Black, Nitrazine Yellow, NitroRed, Nitrosulfonazo III, Solvent Red 26, and Oil Red O. An example of adye is a triphenylmethane stain (e.g., Malachite Green, Crystal Violet,or fuchsine).

An example of a dye is a dye which is an aromatic compound (e.g.,benzene, naphthalene, or anthracene) and has a diazo group. By usingthese dyes, ozone can be specifically detected even in the presence ofanother gas.

An example of a dye is a diazo dye which is an aromatic compound (e.g.,benzene, naphthalene, or anthracene) and has a hydroxyl group, asulfurous acid group, or primary to tertiary amino groups. By usingthese dyes, ozone can be specifically detected even in the presence ofanother gas. In addition, the stability of the dye can be obtained tomore stably detect ozone.

As a method of introducing a dye into a porous material, the porousmaterial is impregnated with the dye by using a solution, and the dye isintroduced into pores and dried. As another method, the dye may beintroduced into pores by vapor deposition. As still another method, thedye may be mixed with another compound and introduced into pores infabricating a porous material by the sol-get method.

According to the third embodiment, the adsorption area of ozone gas tobe detected can be increased by using a sensing element 103 a containingthe dye in the pores of the porous material. Compared to a conventionalmethod, the sensitivity and accumulation capacity can be increased,realizing cumulative use.

The third embodiment has exemplified the use of triethanolamine as anacid gas sorbent. Alternatively, glycerol may be used.

Also in the third embodiment, the porous material preferably has anaverage pore diameter of 20 nm or less.

Fourth Embodiment

An ozone gas sensing element according to the fourth embodiment of thepresent invention will be described.

An ozone gas sensing element fabrication method according to the fourthembodiment will be explained.

As shown in FIG. 1A, a solution is prepared by dissolving Orange II as adye (stain) in water. The Orange II concentration is 0.2%. The trappingand detective solution is filled in a vessel 102. As shown in FIG. 1B, aporous material having an average pore diameter of 4 nm is immersed forabout 2 hrs. The porous material is identical to that described in thefirst embodiment, and is made of Vycor 7930 available from Corning. Theporous material has a chip size of 8 (mm)×8 (mm) with a thickness of 1(mm).

The porous material is immersed in the solution to impregnate thesolution into the porous material. The porous material impregnated withthe solution is extracted from the solution, air-dried, and left driedin a nitrogen gas flow for half a day, thereby fabricating a sensingelement according to the fourth embodiment.

When the fabricated sensing element was exposed to air at an ozoneconcentration of 100 ppb, the orange color visually faded. This changewas measured by an absorptiometer.

The result of measuring the absorbance of the sensing element accordingto the fourth embodiment will be explained with reference to FIG. 9. InFIG. 9, the broken line represents the measurement result of the sensingelement in initial dark orange, and the solid line represents themeasurement result of the sensing element after fading. This change wasirreversible.

The ozone concentration was changed within the range of 100 ppb to 1 ppmto observe almost the same spectrum change except for the lightabsorption intensity.

FIG. 10 shows the absorbance when the sensing element is exposed to airat an ozone concentration of about 20 ppb. In FIG. 10, the broken linerepresents the measurement result of the sensing element in initial darkorange, and the solid line represents the measurement result afterexposure to detection target air. This change was also irreversible.

As shown in FIG. 10, the sensing element according to the fourthembodiment exhibits a decrease in absorption around a wavelength of 510nm. Ozone gas can be detected even in the use of the sensing elementaccording to the fourth embodiment. Ozone gas in air can also bedetected.

The fourth embodiment has exemplified the use of Orange II as a dye.Examples of a dye are Orange I, Orange G, Methyl Orange, Bismarck Brown,Methyl Yellow, Acid Chrome Violet K, Crocein Orange G, Chromotrope FB,New Coccine, Crystal Scarlet, Alizarin Blue Black R, Plasmocorinth B,Sudan II, Sudan III, Sudan IV, Sudan Red B, Sudan Red 7B, Sunset YellowFCF, Toluidine Red, Tropaeoline O, Xylidine Ponceau 2R, zinconmonosodium salt, Benzopurpurin 4B, Biebrich Scarlet Red, Bordeaux R,Brilliant Crocein MOO, 2-(5-bromo-2-pyridylazo) 5-(diethylamino) phenol,6′-butoxy-2,6-diamino-3,3′-azodipyridine, Acid Black 24, Acid Blue 29,Acid Blue 92, Acid Blue 113, Acid Blue 120, Acid Orange 8, Acid Orange51, Acid Orange 63, Acid Orange 74, Acid Red 1, Acid Red 4, Acid Red 8,Acid Red 37, Acid Red 97, Acid Red 114, Acid Red 151, Acid Red 183, AcidViolet 7, Acid Yellow 17, Acid Yellow 25, Acid Yellow 29, Acid Yellow34, Acid Yellow 42, Acid Yellow 76, Acid Yellow 99, Alizarin Yellow GG,Allura Red AC, Amaranth, Calcion, Chicago Sky Blue 6B, Chromotrope 2B,Chromotrope 2R, chrysoidin, Congo Red, Direct Blue 71, Direct Red 23,Direct Red 75, Direct Red 80, Direct Red 81, Direct Violet 51, DirectYellow 50, Direct Yellow 62, Disperse Red 1, Disperse Red 19, DisperseYellow 3, Eriochrome Blue Black B, Eriochrome Black T, Evans Blue, FatBrown RR, Metanil Yellow, Naphthol Blue Black, Nitrazine Yellow, NitroRed, Nitrosulfonazo III, Solvent Red 26, and Oil Red O. An example of adye is a dye which is an aromatic compound (e.g., benzene, naphthalene,or anthracene) and has a diazo group. By using these dyes, ozone can bespecifically detected even in the presence of another gas.

An example of a dye is a diazo dye which contains a dye as an aromaticcompound (e.g., benzene, naphthalene, or anthracene) having a diazogroup and has a hydroxyl group, a sulfurous acid group, or primary totertiary amino groups. By using these dyes, ozone can be specificallydetected even in the presence of another gas. In addition, the stabilityof the dye can be obtained to more stably detect ozone.

As a method of introducing a dye into the pores of a porous material,the porous material is impregnated with the dye by using a trapping anddetective solution, and the dye is introduced into pores and dried. Asanother method, the dye may be introduced into pores by vapordeposition. As still another method, the dye may be mixed with anothercompound and introduced into pores in fabricating a porous material bythe sol-get method.

According to the fourth embodiment, the adsorption area of ozone gas tobe detected can be increased by using a sensing element 103 a containingthe dye in the pores of the porous material. Compared to a conventionalmethod, the sensitivity and accumulation capacity can be increased,realizing cumulative use.

Also in the fourth embodiment, the porous material preferably has anaverage pore diameter of 20 nm or less.

Fifth Embodiment

An ozone gas sensing element according to the fifth embodiment of thepresent invention will be described.

An ozone gas sensing element fabrication method according to the fifthembodiment will be explained.

As shown in FIG. 1A, an aqueous solution of 0.3% of indigo carminedisodium salt and 1 N of hydrochloric acid is prepared as a solution 101by dissolving indigo carmine disodium salt as a dye (stain) in water andadding hydrochloric acid as an acid. The solution 101 is filled in avessel 102.

As shown in FIG. 1B, a porous material 103 is immersed in the solution101. An example of the porous material 103 is porous glass having anaverage pore diameter of 4 nm. The porous material 103 is identical tothat described in the first embodiment, and is made of Vycor 7930available from Corning. The porous material has a chip size of 8 (mm)×8(mm) with a thickness of 1 (mm).

The porous material 103 is immersed in the solution 101 for 24 hrs toimpregnate the pores of the porous material 103 with the solution 101.The porous material impregnated with the solution 101 is extracted fromthe solution, and air-dried. As shown in FIG. 1C, the porous material isleft dried in a nitrogen gas flow for 24 hrs or more, therebyfabricating a sensing element 103 a according to the fifth embodiment.

As shown in FIG. 1D, the absorbance of the sensing element 103 a in thedirection of thickness is measured. In FIG. 1E, the sensing element 103a is exposed for 2 hrs to detection target air 104 containing ozone at aconcentration of, e.g., 20 ppb. The sensing element 103 a is extractedfrom the detection target air 104. As shown in FIG. 1F, the absorbanceof the sensing element 103 a in the direction of thickness is measuredagain.

The result of two absorbance measurements (absorbance analyses) will beexplained with reference to FIG. 11. No absorbance is measured at atransmitted light measurement wavelength of 350 nm or less because lightis absorbed by porous glass (Vycor 7930) which constitutes the sensingelement.

In FIG. 11, the broken line represents the absorbance before exposure todetection target air. The solid line represents the absorbance afterexposure to detection target air. A large difference is found betweenthe solid and broken lines in a wavelength range of 500 nm to 700 nm,particularly around 600 nm. In measurement of the absorbance afterexposure to detection target air, absorption decreases at a wavelengthof 600 nm. The absorbance can be estimated to decrease because the dyein the sensing element is decomposed to produce a new decompositionproduct upon exposure to detection target air. This product can beestimated to be produced by decomposing a C═C bond contained in themolecular skeleton of indigo carmine disodium salt.

The absorbance of the sensing element at 600 nm obtained when nohydrochloric acid is added to the trapping and detective solution is1/100 of the absorbance of the sensing element at 600 nm obtained whenhydrochloric acid is added to the solution. Addition of hydrochloricacid increases the absorbance around 600 nm. Many dye components areestimated to enter the porous material.

As shown in FIG. 3, a sensing element fabricated by the above-describedmanufacturing method functions as an adsorbent having a transparentmatrix shape with a plurality of pores 301 at an average pore diameterof, e.g., 20 nm or less. At least some pores 301 in a porous material305 are coupled to pores on the surface of the porous material. The dyeis deposited in the pore 301 of a sensing element 302. The porousmaterial is exposed to air, and then moisture in air is adsorbed in thepore to form a thin water film. As a result, a thin film 303 of anaqueous solution (trapping and detective solution) in which the dye isdissolved can be estimated to be formed on the inner wall of the pore301 of the sensing element 302. At least some pores 301 are coupled topores on the surface of the porous material, so the dye can be estimatedto be deposited in at least some pores.

An ozone molecule 304 which enters the pore 301 of the sensing element302 reacts with the dye to decompose a carbon-carbon double bond. Thatis, the π-electron system extending over the molecule is split into twoor more. The split molecule does not absorb any light around 600 nm, andthe color of the sensing element fades. That is, the dye causes fadingreaction with ozone. At least some pores 301 are coupled to pores on thesurface of the porous material, and ozone gas is estimated to react withthe dye deposited in at least some pores.

The absorption spectrum is measured using, e.g., a spectrophotometer(absorptiometer) to achieve quantitative measurement of the decomposedmolecule. By quantitative measurement, ozone gas can be indirectlymeasured.

For example, a porous material is made of a material which transmitslight in the light absorption wavelength region of the dye. The lightabsorption characteristic of the sensing element which adsorbs ozone gascan be measured. By measuring the light absorption characteristic, theadsorbed ozone gas can be detected.

Similar to the method described in the first embodiment, the absorbancecan be measured by fixing the sensing element 103 a of the fifthembodiment to the thin film measurement holder of the absorptiometer.Quantitative measurement at ppb level can be achieved by obtaining therelationship between the difference in absorbance and the concentrationfrom measurement of the absorbance.

As described in the first embodiment, a change in absorbance at themaximum absorption wavelength per exposure amount (concentration(ppb)×exposure time (h)) is obtained as the sensitivity index. As shownin FIG. 11, a change in absorbance after exposure to 20-ppb ozone gasfor 2 hrs is 0.009. The sensitivity index is 2.5×10⁻⁴ ppb⁻¹·hr⁻¹, andvery high sensitivity can be attained.

As described above, the fifth embodiment prepares a sensing element inwhich a mixture of an acid and a dye (stain) that changes in theabsorbance of the visible region upon reaction with ozone gas isdeposited in the pores of a transparent porous material. It is estimatedthat, when the sensing element is exposed to an ozone gas-containingatmosphere, a double bond such as C═C in the dye is broken by ozone gasadsorbed in the pores of the sensing element, and the structure andelectron state of the dye molecule change to change the absorptionspectrum of the visible region. Thus, ozone gas can be detected when thecolor of the sensing element changes and the first and secondtransmittances become different.

The fifth embodiment has exemplified the use of indigo carmine disodiumsalt as a dye. An example of a dye is an indigoid stain having indigo(e.g., indigo or indigo carmine tripotassium salt).

Examples of a dye are Orange I, Orange II, Orange G, Methyl Orange,Bismarck Brown, Methyl Yellow, Acid Chrome Violet K, Crocein Orange G.Chromotrope FB, New Coccine, Crystal Scarlet, Alizarin Blue Black R,Plasmocorinth B, Sudan II, Sudan III, Sudan IV, Sudan Red B, Sudan Red7B, Sunset Yellow FCF, Toluidine Red, Tropaeoline O, Xylidine Ponceau2R, zincon monosodium salt, Benzopurpurin 4B, Biebrich Scarlet Red,Bordeaux R, Brilliant Crocein MOO, 2-(5-bromo-2-pyridylazo)5-(diethylamino) phenol, 6′-butoxy-2,6-diamino-3,3′-azodipyridine, AcidBlack 24, Acid Blue 29, Acid Blue 92, Acid Blue 113, Acid Blue 120, AcidOrange 8, Acid Orange 51, Acid Orange 63, Acid Orange 74, Acid Red 1,Acid Red 4, Acid Red 8, Acid Red 37, Acid Red 97, Acid Red 114, Acid Red151, Acid Red 183, Acid Violet 7, Acid Yellow 17, Acid Yellow 25, AcidYellow 29, Acid Yellow 34, Acid Yellow 42, Acid Yellow 76, Acid Yellow99, Alizarin Yellow GG, Allura Red AC, Amaranth, Calcion, Chicago SkyBlue 6B, Chromotrope 2B, Chromotrope 2R, chrysoidin, Congo Red, DirectBlue 71, Direct Red 23, Direct Red 75, Direct Red 80, Direct Red 81,Direct Violet 51, Direct Yellow 50, Direct Yellow 62, Disperse Red 1,Disperse Red 19, Disperse Yellow 3, Eriochrome Blue Black B. EriochromeBlack T, Evans Blue, Fat Brown RR, Metanil Yellow, Naphthol Blue Black,Nitrazine Yellow, Nitro Red, Nitrosulfonazo III, Solvent Red 26, and OilRed O. An example of a dye is a dye which is an aromatic compound (e.g.,benzene, naphthalene, or anthracene) and has a diazo group. By usingthese dyes, ozone can be specifically detected even in the presence ofanother gas.

An example of a dye is a diazo dye which contains a dye as an aromaticcompound (e.g., benzene, naphthalene, or anthracene) having a diazogroup and has a hydroxyl group, and has a hydroxyl group, a sulfurousacid group, or primary to tertiary amino groups. By using these dyes,ozone can be specifically detected even in the presence of another gas.In addition, the stability of the dye can be obtained to more stablydetect ozone.

As a method of introducing a dye into the pores of a porous material,the porous material is impregnated with the dye serving as a solution,and the dye is introduced into pores and dried. As another method, thedye may be introduced into pores by vapor deposition. As still anothermethod, the dye may be mixed with another compound and introduced intopores in fabricating a porous material by the sol-get method.

According to the fifth embodiment, the adsorption area of ozone gas tobe detected can be increased by using the sensing element containing thedye in the pores of the porous material. Compared to a conventionalmethod, the sensitivity and accumulation capacity can be increased,realizing cumulative use.

According to the fifth embodiment, as shown in FIG. 4, the lighttransmittance of the sensing element at a predetermined wavelengthincreases as the ozone gas concentration in measurement target airincreases. The predetermined wavelength is about 600 nm.

The fifth embodiment can detect ozone gas from an optical change byusing the compact sensing element 103 a, and can very easily detectozone gas at high precision. In absorbance measurement, only a change insingle peak suffices to be monitored, and measurement is easy.

When the sensing element was made of porous glass (borosilicate glass),light passed in the visible light region (350 nm to 800 nm) inmeasurement of the transmission spectrum in the UV visible wavelengthregion (wavelength: 200 nm to 2,000 nm) by setting the average porediameter to 20 nm or less. For a larger average pore diameter, an abruptdecrease in transmittance in the visible region was observed. Hence, theabove-described porous material desirably has an average pore diameterof 20 nm or less. A transparent porous material is desirably used in avisible region of 350 nm to 800 nm. In the fifth embodiment, thespecific surface of the porous material is 100 m² or more per g.

In the fifth embodiment, the solution 101 is prepared by addinghydrochloric acid as an acid. Any one of acetic acid, sulfuric acid, andphosphoric acid may be used.

Sixth Embodiment

An ozone gas sensing element according to the sixth embodiment of thepresent invention will be described.

An ozone gas sensing element fabrication method according to the sixthembodiment will be explained.

As shown in FIG. 1A, a solution is prepared by dissolving, in water,indigo carmine disodium salt as a dye (stain), and hydrochloric acid andglycerol as an acid gas sorbent. The indigo carmine disodium saltconcentration is 0.4%, the hydrochloric acid concentration is 1 N, andthe glycerol concentration is 1.0%.

As shown in FIG. 1B, a porous material having an average pore diameterof 4 nm is immersed in the dye solution. The porous material isidentical to that described in the first embodiment, and is made ofVycor 7930 available from Corning. The porous material has a chip sizeof 8 (mm)×8 (mm) with a thickness of 1 (mm).

The porous material is immersed in the dye solution for 24 hrs toimpregnate the pores of the porous material with the dye solution. Theporous material is air-dried, and then left dried in a dry air flow fora day, thereby fabricating a sensing element according to the sixthembodiment.

The absorbance of the sensing element fabricated in this manneraccording to the sixth embodiment was measured.

Absorption spectra before and after exposing the sensing element of thesixth embodiment to measurement target air will be described withreference to FIG. 12. In FIG. 12, the broken line represents theabsorption spectrum before exposure to measurement target air. The solidline represents the absorption spectrum after exposure for 2 hrs to aircontaining ozone gas at a concentration of 100 ppb.

As shown in FIG. 12, the sensing element of the sixth embodimentrepresented by the solid line exhibits a decrease in absorption around awavelength of 600 nm. This decrease is about 0.05, and ozone gas can bedetected at high-sensitivity ppb level.

In the above-described fabrication method, a comparative sensing elementwas fabricated except glycerol. The influence of disturbance of NO₂ asan acid gas was investigated using the comparative sensing element. As aresult, the comparative sensing element observed disturbance of NO₂, butthe sensing element of the sixth embodiment did not observe anydisturbance of NO₂.

As described above, the sixth embodiment prepares a sensing element inwhich a mixture of an acid, glycerol, and a dye that changes in theabsorbance of the visible region upon reaction with ozone gas isdeposited in the pores of a transparent porous material. It is estimatedthat, when the sensing element is exposed to an atmosphere containingozone gas and many acid gases other than ozone, a carbon-carbon doublebond in an indigo ring contained in the dye is broken by ozone gasdeposited in the pores of the sensing element almost free fromdisturbance of an acid gas, and the electron state of the dye moleculechanges to change the absorption spectrum of the visible region. Forthis reason, ozone gas can be detected when the color of the sensingelement changes and the first and second transmittances becomedifferent.

The sixth embodiment has exemplified the use of indigo carmine disodiumsalt as a dye. An example of a dye is an indigoid stain having indigo(e.g., indigo or indigo carmine tripotassium salt).

As a method of introducing a dye into the pores of a porous material,the porous material is impregnated with the dye serving as a solutionand dried. As another method, the dye may be introduced into pores byvapor deposition. As still another method, the dye may be mixed withanother compound and introduced into pores in fabricating a porousmaterial by the sol-get method.

According to the sixth embodiment, the adsorption area of ozone gas tobe detected can be increased by using the sensing element containing thedye in the pores of the porous material. Compared to a conventionalmethod, the sensitivity and accumulation capacity can be increased,realizing cumulative use.

Also in the sixth embodiment, the porous material desirably has anaverage pore diameter of 20 nm or less.

In the sixth embodiment, glycerol is added as an acid gas sorbent.Instead, triethanolamine may be added.

Seventh Embodiment

An ozone gas sensing element according to the seventh embodiment of thepresent invention will be described.

An ozone gas sensing element fabrication method according to the seventhembodiment will be explained.

As shown in FIG. 1A, a dye solution is prepared by dissolving, in water,indigo carmine disodium salt as a dye (stain), acetic acid as an acid,and glycerol as a hygroscopic compound. The indigo carmine disodium saltconcentration is 0.4%, the acetic acid concentration is 1 N, and theglycerol concentration is 10.0%.

As shown in FIG. 1B, a porous material having an average pore diameterof 4 nm is immersed in the dye solution. The porous material isidentical to that described in the first embodiment, and is made ofVycor 7930 available from Corning. The porous material has a chip sizeof 8 (mm)×8 (mm) with a thickness of 1 (mm). The porous material isimmersed in the dye solution for 24 hrs to impregnate the pores of theporous material with the dye solution, and then air-dried. The porousmaterial is left dried in a nitrogen gas flow for a day, therebyfabricating a sensing element according to the seventh embodiment.

Absorption spectra before and after exposing the sensing element of theseventh embodiment to measurement target air will be described withreference to FIG. 13. In FIG. 13, the broken line represents theabsorption spectrum before exposure to measurement target air. The solidline represents the absorption spectrum after exposing the sensingelement of the seventh embodiment for 2 hrs to air containing ozone gasat a concentration of 100 ppb.

In the seventh embodiment, as shown in FIG. 13, the solid line exhibitsa decrease in absorption around a wavelength of 600 nm. This decrease isabout 0.05, and ozone gas can be detected at high-sensitivity ppb level.

In the above-described fabrication method, a comparative sensing elementwas fabricated except glycerol. The influence of disturbance of ahumidity change was investigated using the comparative sensing element.As a result, the comparative sensing element observed disturbance ofhumidity, but the sensing element of the seventh embodiment hardlyobserved disturbance.

As described above, the seventh embodiment prepares a sensing element inwhich an acid, hygroscopic compound, and a dye that irreversibly changesin the absorbance of the visible region upon reaction with ozone gas aredeposited in the pores of a transparent porous material. It is estimatedthat, when the sensing element is exposed to an ozone gas-containingatmosphere, a double bond such as C═C in the dye is broken by ozone gasadsorbed in the pores of the sensing element, and the electron state ofthe dye molecule changes to change the absorption spectrum of thevisible region.

Ozone gas can be detected when the color of the sensing element changesand the first and second transmittances become different.

Since the hygroscopic compound contains water, even addition of moistureupon a humidity change has little influence. Thus, disturbance ofhumidity can be reduced.

The seventh embodiment has exemplified the use of indigo carminedisodium salt as a dye. An example of a dye is an indigoid stain havingan indigo ring (e.g., indigo or indigo carmine tripotassium salt).

Examples of a dye are Orange I, Orange II, Orange G, Methyl Orange,Bismarck Brown, Methyl Yellow, Acid Chrome Violet K, Crocein Orange G,Chromotrope FB, New Coccine, Crystal Scarlet, Alizarin Blue Black R.Plasmocorinth B, Sudan II, Sudan III, Sudan IV, Sudan Red B, Sudan Red7B, Sunset Yellow FCF, Toluidine Red, Tropaeoline O, Xylidine Ponceau2R, zincon monosodium salt, Benzopurpurin 4B, Biebrich Scarlet Red,Bordeaux R, Brilliant Crocein MOO, 2-(5-bromo-2-pyridylazo)5-(diethylamino) phenol, 6′-butoxy-2,6-diamino-3,3′-azodipyridine, AcidBlack 24, Acid Blue 29, Acid Blue 92, Acid Blue 113, Acid Blue 120, AcidOrange 8, Acid Orange 51, Acid Orange 63, Acid Orange 74, Acid Red 1,Acid Red 4, Acid Red 8, Acid Red 37, Acid Red 97, Acid Red 114, Acid Red151, Acid Red 183, Acid Violet 7, Acid Yellow 17, Acid Yellow 25, AcidYellow 29, Acid Yellow 34, Acid Yellow 42, Acid Yellow 76, Acid Yellow99, Alizarin Yellow GG, Allura Red AC, Amaranth, Calcion, Chicago SkyBlue 6B, Chromotrope 2B, Chromotrope 2R, chrysoidin, Congo Red, DirectBlue 71, Direct Red 23, Direct Red 75, Direct Red 80, Direct Red 81,Direct Violet 51, Direct Yellow 50, Direct Yellow 62, Disperse Red 1,Disperse Red 19, Disperse Yellow 3, Eriochrome Blue Black B, EriochromeBlack T, Evans Blue, Fat Brown RR, Metanil Yellow, Naphthol Blue Black,Nitrazine Yellow, Nitro Red, Nitrosulfonazo III, Solvent Red 26, and OilRed O. An example of a dye is a dye which is an aromatic compound (e.g.,benzene, naphthalene, or anthracene) and has a diazo group. By usingthese dyes, ozone can be specifically detected even in the presence ofanother gas.

An example of a dye is a diazo dye which contains a dye as an aromaticcompound (e.g., benzene, naphthalene, or anthracene) having a diazogroup and has a hydroxyl group, a sulfurous acid group, or primary totertiary amino groups. By using these dyes, ozone can be specificallydetected even in the presence of another gas. In addition, the stabilityof the dye can be obtained to more stably detect ozone.

In the seventh embodiment, the dye solution 101 is prepared by addingacetic acid as an acid. Any one of hydrochloric acid, sulfuric acid, andphosphoric acid may be used.

In the seventh embodiment, the dye solution 101 is prepared by addingglycerol as a hygroscopic compound. Alternatively, ethylene glycol maybe used.

As a method of introducing a dye into the pores of a porous material,the porous material is impregnated with the dye by using the dyesolution, and the dye is introduced into pores and dried. As anothermethod, the dye may be introduced into pores by vapor deposition. Asstill another method, the dye may be mixed with another compound andintroduced into pores in fabricating a porous material by the sol-getmethod.

According to the seventh embodiment, the adsorption area of ozone gas tobe detected can be increased by using the sensing element containing thedye in the pores of the porous material. Compared to a conventionalmethod, the sensitivity and accumulation capacity can be increased,realizing cumulative use.

Also in the seventh embodiment, the porous material preferably has anaverage pore diameter of 20 nm or less.

Eighth Embodiment

An ozone gas sensing element according to the eighth embodiment of thepresent invention will be described.

An ozone gas sensing element fabrication method according to the eighthembodiment will be explained.

As shown in FIG. 1A, a dye solution is prepared by dissolving, in water,indigo carmine disodium salt as a dye (stain), and phosphoric acid andsodiumdihydrogenphosphate dehydrate as a buffer. The indigo carminedisodium salt concentration is 0.4%, the phosphoric acid concentrationis 50 mmol, and the sodiumdihydrogenphosphate dehydrate concentration is50 mmol.

As shown in FIG. 1B, a porous material having an average pore diameterof 4 nm is immersed in the dye solution. The porous material isidentical to that described in the first embodiment, and is made ofVycor 7930 available from Corning. The porous material has a chip sizeof 8 (mm)×8 (mm) with a thickness of 1 (mm). The porous material isimmersed in the dye solution for 24 hrs to impregnate the pores of theporous material with the dye solution, and then air-dried. The porousmaterial is left dried in a nitrogen gas flow for a day, therebyfabricating a sensing element according to the eighth embodiment.

Absorption spectra before and after exposing the sensing element of theeighth embodiment to measurement target air will be described withreference to FIG. 14. In FIG. 14, the broken line represents theabsorption spectrum before exposure to measurement target air. The solidline represents the absorption spectrum after exposing the sensingelement of the eighth embodiment for 2 hrs to air containing ozone gasat a concentration of 100 ppb.

In the eighth embodiment, as shown in FIG. 14, the solid line exhibits adecrease in absorption around a wavelength of 600 nm. This decrease isabout 0.05, and ozone gas can be detected at high-sensitivity ppb level.

In the above-described fabrication method, a comparative sensing elementwas fabricated except a buffer. The influence of disturbance of ahumidity change was investigated using the comparative sensing element.As a result, the comparative sensing element observed disturbance ofhumidity, but the sensing element of the eighth embodiment hardlyobserved disturbance.

As described above, the eighth embodiment prepares a sensing element inwhich a mixture of a buffer and a dye that changes in the absorbance ofthe visible region upon reaction with ozone gas is deposited in thepores of a transparent porous material. It is estimated that, when thesensing element is exposed to an ozone gas-containing atmosphere, acarbon-carbon double bond in an indigo ring contained in the dye isbroken by ozone gas deposited in the pores of the sensing element, andthe electron state of the dye molecule changes to change the absorptionspectrum of the visible region. Hence, ozone gas can be detected whenthe color of the sensing element changes and the first and secondtransmittances become different.

By adding the buffer, the hydrogen ion concentration can be keptconstant even upon addition of moisture by a humidity change, anddisturbance of humidity can be reduced.

The seventh embodiment has exemplified the use of indigo carminedisodium salt as a dye. An example of a dye is an indigoid stain havingan indigo ring (e.g., indigo or indigo carmine tripotassium salt).

Examples of a dye are Orange I, Orange II, Orange G, Methyl Orange,Bismarck Brown, Methyl Yellow, Acid Chrome Violet K, Crocein Orange G,Chromotrope FB, New Coccine, Crystal Scarlet, Alizarin Blue Black R,Plasmocorinth B, Sudan II, Sudan III, Sudan IV, Sudan Red B, Sudan Red7B, Sunset Yellow FCF, Toluidine Red, Tropaeoline O, Xylidine Ponceau2R, zincon monosodium salt, Benzopurpurin 4B, Biebrich Scarlet Red,Bordeaux R, Brilliant Crocein MOO, 2-(5-bromo-2-pyridylazo)5-(diethylamino) phenol, 6′-butoxy-2,6-diamino-3,3′-azodipyridine, AcidBlack 24, Acid Blue 29, Acid Blue 92, Acid Blue 113, Acid Blue 120, AcidOrange 8, Acid Orange 51, Acid Orange 63, Acid Orange 74, Acid Red 1,Acid Red 4, Acid Red 8, Acid Red 37, Acid Red 97, Acid Red 114, Acid Red151, Acid Red 183, Acid Violet 7, Acid Yellow 17, Acid Yellow 25, AcidYellow 29, Acid Yellow 34, Acid Yellow 42, Acid Yellow 76, Acid Yellow99, Alizarin Yellow GG, Allura Red AC, Amaranth, Calcion, Chicago SkyBlue 6B, Chromotrope 2B, Chromotrope 2R, chrysoidin, Congo Red, DirectBlue 71, Direct Red 23, Direct Red 75, Direct Red 80, Direct Red 81,Direct Violet 51, Direct Yellow 50, Direct Yellow 62, Disperse Red 1,Disperse Red 19, Disperse Yellow 3, Eriochrome Blue Black B, EriochromeBlack T, Evans Blue, Fat Brown RR, Metanil Yellow, Naphthol Blue Black,Nitrazine Yellow, Nitro Red, Nitrosulfonazo III, Solvent Red 26, and OilRed O. An example of a dye is a dye which is an aromatic compound (e.g.,benzene, naphthalene, or anthracene) and has a diazo group. By usingthese dyes, ozone can be specifically detected even in the presence ofanother gas.

An example of a dye is a diazo dye which contains a dye as an aromaticcompound (e.g., benzene, naphthalene, or anthracene) having a diazogroup and has a hydroxyl group, a sulfurous acid group, or primary totertiary amino groups. By using these dyes, ozone can be specificallydetected even in the presence of another gas. In addition, the stabilityof the dye can be obtained to more stably detect ozone.

As a method of introducing a dye into the pores of a porous material,the porous material is impregnated with the dye by using the dyesolution, and the dye is introduced into pores and dried. As anothermethod, the dye may be introduced into pores by vapor deposition. Asstill another method, the dye may be mixed with another compound andintroduced into pores in fabricating a porous material by the sol-getmethod.

According to the eighth embodiment, the adsorption area of ozone gas tobe detected can be increased by using the sensing element containing thedye in the pores of the porous material. Compared to a conventionalmethod, the sensitivity and accumulation capacity can be increased,realizing cumulative use.

Also in the eighth embodiment, the porous material preferably has anaverage pore diameter of 20 nm or less.

The first to eighth embodiments have described a plate-like sensingelement. The sensing element is not limited to this, and may be shapedinto a fiber.

In the above-described embodiments, the dye (stain) is deposited in thepores of a porous material.

The present invention is not limited to the porous material, and canemploy any material as far as dye states before and after reaction withozone can be measured.

Ninth Embodiment

The ninth embodiment of the present invention will be described.

As shown in FIG. 15, an ozone gas detection apparatus (measurementapparatus) according to the ninth embodiment comprises a light-emittingunit 1001 which emits light having a predetermined wavelength, a sensingelement 1002 which senses light emitted by the light-emitting unit 1001,a light-detecting unit 1003 which is connected to the sensing element1002 and receives light having passed through the sensing element 1002,and a signal processing unit 1008 which is connected to thelight-detecting unit 1003.

The signal processing unit 1008 comprises a conversion/amplifying unit1004 which is connected to the light-detecting unit 1003, an A/Dconversion unit 1005 which is connected to the conversion/amplifyingunit 1004, an output detection unit 1006 which is connected to the A/Dconversion unit 1005, and an arithmetic unit 1007 which is connected tothe output detection unit 1006.

For example, the sensing element 1002 is irradiated with light emittedby the light-emitting unit 1001 which is constituted by an LED foremitting light having a predetermined wavelength. Light having passedthrough the sensing element 1002 is received by the light-detecting unit1003. The light-detecting unit 1003 photoelectrically converts receivedlight and outputs a signal current. The conversion/amplifying unit 1004amplifies the output signal current, and converts the current into avoltage. The A/D conversion unit 1005 converts the voltage signal into adigital signal. The output detection unit 1006 outputs the digitalsignal as a detection result. The arithmetic unit 1007 calculates anozone gas amount on the basis of the signal output from the outputdetection unit 1006 and the light absorption characteristic, obtained inadvance, of the sensing element which contains a dye 303 before reactionwith ozone gas 304.

The sensing element 1002 is a sensing element according to any one ofthe first to eighth embodiments described above. The light-emitting unit1001 can adopt a blue LED having an emission wavelength of, e.g., 470nm.

For example, ozone gas was detected in a dry air atmosphere and air atan ozone concentration of 50 ppb to 500 ppb by using a detectionapparatus (measurement apparatus) having a sensing element according tothe first embodiment.

It is estimated that, when ozone gas enters the pores of the sensingelement and adsorbed, a double bond such as N═N or C═C in the dye isbroken, and the electron state of the dye molecule changes to change thecolor of the sensing element. As a result, the absorption spectrum ofthe visible range changes. Light emitted by the light-emitting unit 1001enters the light-receiving unit 1003 via the sensing element 1002, and achange in the color of the sensing element 1002 can be measured as achange in electrical signal output from the light-receiving unit 1003 byan electric instrument which performs signal processing.

Consequently, as described above, an output different from the initialstate in which the sensing element is not exposed to ozone gas can beobtained.

According to the ninth embodiment, the ozone gas detection apparatus(measurement apparatus) can be easily constituted.

As described above, the ozone gas sensing element according to thepresent invention comprises a porous material, and a dye which isdeposited in the pores of the porous material and changes in the lightabsorption characteristic of the visible region upon reaction with ozonegas. With this arrangement, when ozone gas enters the pores of the ozonegas sensing element and is adsorbed, the dye is decomposed to fade thecolor of the ozone gas sensing element. By checking a color change,ozone gas can be detected. Ozone gas can be detected more easily athigher precision than a conventional method.

A dye which is an aromatic compound (e.g., benzene, naphthalene, oranthracene) and has a diazo group can specifically detect ozone even inthe presence of another gas.

A dye which is an aromatic compound (e.g., benzene, naphthalene, oranthracene) and has a hydroxyl group, a sulfurous acid group, or primaryto tertiary amino groups in addition to a diazo group can specificallydetect ozone even in the presence of another gas. Further, the stabilityof the dye can be obtained to more stably detect ozone.

When a triphenylmethane stain dye is used as a dye, ozone can bespecifically detected even in the presence of another gas.

When a fuchsonimine-containing dye is used as a dye, ozone can bespecifically detected even in the presence of another gas.

When an indigoid stain having an indigo ring is used as a dye, ozone canbe specifically detected even in the presence of another gas.

Since a triphenylmethane stain dye or fuchsonimine dye and alkali aredeposited in the pores of the porous material, the absorbance can bestabilized even in nitrogen without any change.

Since a dye and acid gas sorbent are deposited in the pores of theporous material, ozone can be detected without disturbance by NO₂. Asthe acid gas sorbent, either of glycerol and triethanolamine can beemployed. The average pore diameter of the porous material is set to 20nm or less at which the dye can enter pores. In measurement of theabsorption spectrum in the UV visible wavelength region (wavelength of200 nm to 2,000 nm), a larger quantity of light can be transmitted inthe visible light region (350 nm to 800 nm).

A diazo dye or indigoid dye and an acid are deposited in the pores ofthe porous material. With this arrangement, when ozone gas enters thepores of the ozone gas sensing element and is adsorbed, the dye isdecomposed to fade the color of the ozone gas sensing element. Bychecking a color change, ozone gas can be detected. Ozone gas can bedetected more easily at higher precision than a conventional method.

In the ozone gas sensing element, an acid is selected as one ofhydrochloric acid, acetic acid, sulfuric acid, and phosphoric acid. Manydye components can be mixed in the porous material.

In the ozone gas sensing element, glycerol is deposited together withthe dye and acid in the pores of the porous material, thus preventingdisturbance of NO₂.

In the ozone gas sensing element, the average pore diameter of theporous material is set to less than 20 nm at which the dye can enterpores. In measurement of the absorption spectrum in the UV visiblewavelength region (wavelength of 200 nm to 2,000 nm), a larger quantityof light can be transmitted in the visible light region (350 nm to 800nm).

A diazo dye or indigoid dye, an acid, and a hygroscopic compound aredeposited in the pores of the porous material. With this arrangement,when ozone gas enters the pores of the ozone gas sensing element and isadsorbed, the dye is decomposed to fade the color of the ozone gassensing element. By checking a color change, ozone gas can be detected.Ozone gas can be detected more easily at higher precision than aconventional method.

In the ozone gas sensing element, an acid is selected as one ofhydrochloric acid, acetic acid, sulfuric acid, and phosphoric acid. Manydye components can be mixed in the porous material.

In the ozone gas sensing element, examples of a hygroscopic componentare glycerol and ethylene glycol. A large amount of water can be held inthe porous material to reduce the influence of humidity.

In the ozone gas sensing element, the average pore diameter of theporous material is set to less than 20 nm at which the dye can enterpores. In measurement of the absorption spectrum in the UV visiblewavelength region (wavelength of 200 nm to 2,000 nm), a larger quantityof light can be transmitted in the visible light region (350 nm to 800nm).

A diazo dye or indigoid dye and a buffer are deposited in the pores ofthe porous material. With this arrangement, when ozone gas enters thepores of the ozone gas sensing element and is adsorbed, the dye isdecomposed to fade the color of the ozone gas sensing element. Bychecking a color change, ozone gas can be detected. Ozone gas can bedetected more easily at higher precision than a conventional method.

Since the buffer is introduced in the ozone gas sensing element, thehydrogen ion concentration in the porous material can be maintainedalmost free from the influence of humidity.

In the ozone gas sensing element, the average pore diameter of theporous material is set to less than 20 nm at which the dye can enterpores. In measurement of the absorption spectrum in the UV visiblewavelength region (wavelength of 200 nm to 2,000 nm), a larger quantityof light can be transmitted in the visible light region (350 nm to 800nm).

The adsorption area of ozone gas to be detected can be increased byusing the sensing element containing a dye in the pores of the porousmaterial. Compared to a conventional method, the sensitivity andaccumulation capacity can be increased, realizing cumulative use.

The ozone gas detection apparatus (measurement apparatus) of the presentinvention comprises a light-emitting unit, light-detecting unit, sensingelement, and signal processing unit. The light-emitting unit emits lighthaving a predetermined wavelength. The sensing element is interposedbetween the light-emitting unit and the light-detecting unit, andcomprises a porous material, and a dye which is deposited in the poresof the porous material and changes in the light absorptioncharacteristic of the visible region upon reaction with ozone gas. Thelight-detecting unit comprises a light-receiving surface which isarranged to face the light-emitting unit. The light-detecting unitreceives, via the sensing element, light emitted by the light-emittingunit, and outputs a signal corresponding to a light quantity received bythe light-receiving surface. The signal processing unit calculates anozone gas amount on the basis of the signal output from thelight-detecting unit and the light absorption characteristic, obtainedin advance, of the sensing element which contains a dye before reactionwith ozone gas.

With this arrangement, when ozone gas enters the pores of the sensingelement and is adsorbed, the dye is decomposed to fade the color of thesensing element. Light emitted by the light-emitting unit enters thelight-detecting unit via the sensing element. A change in the color ofthe sensing element is measured as a change in electrical signal outputfrom the light-detecting unit by an electric instrument.

The ozone gas detection apparatus (measurement apparatus) can bearranged in a measurement target atmosphere to detect ozone gas at highprecision. Compared to a conventional method, ozone gas can be detectedmore easily at higher precision.

For example, the light-emitting unit is constituted by a light-emittingdiode, and the light-detecting unit is constituted by a phototransistor.Further, the detection apparatus comprises a battery which suppliespower to the light-emitting diode and phototransistor, a switch whichsupplies or stops power from the battery to the light-emitting diode andphototransistor, and a voltmeter serving as an electric instrument whichis connected between the phototransistor and the battery. The detectionapparatus also comprises a terminal strip having terminals forconnecting the light-emitting diode, phototransistor, battery, switch,and voltmeter, and a board on which the light-emitting diode,phototransistor, battery, switch, voltmeter, and terminal strip arearranged.

Accordingly, a high-precision ozone gas detection apparatus (measurementapparatus) can be constituted within a small area. A commerciallyavailable battery can be used as a power supply, and ozone gas can bemore easily detected.

An ozone gas detection method (measurement method) according to thepresent invention comprises the step of preparing a sensing element inwhich a dye that changes in the light absorption characteristic of thevisible region upon reaction with ozone gas is deposited in the pores ofa porous material, the step of exposing the sensing element to ameasurement environment for a predetermined time, and the step ofmeasuring an ozone gas amount in a measurement target gas on the basisof a change in dye before and after exposing the sensing element to themeasurement environment for a predetermined time. More specifically, theozone gas detection method (measurement method) comprises the first stepof measuring the light transmittance of a sensing element according tothe present invention to obtain the first transmittance, the second stepof exposing the sensing element to a measurement target gas for apredetermined time, the third step of measuring the light transmittanceof the sensing element to obtain the second transmittance, and thefourth step of detecting ozone in the measurement target from thedifference between the first and second transmittances.

With these steps, when the sensing element is exposed to an ozonegas-containing atmosphere, the dye adsorbed in the pores of the sensingelement is decomposed. The color of the sensing element changes togenerate a difference between the first and second transmittances. Thus,ozone gas can be detected. Only a change in the color of the sensingelement is observed after the sensing element is exposed to ameasurement target atmosphere. Ozone gas can be detected more easily athigher precision than a conventional method.

1. An ozone gas measurement apparatus comprising: a light-emitting unit;a light-detecting unit; a sensing element; and a signal processing unit,wherein said light-emitting unit emits light having a predeterminedwavelength, said sensing element is interposed between saidlight-detecting unit and said light-receiving unit, and comprises aporous material, and a dye which is deposited in a pore of the porousmaterial and changes in a light absorption characteristic of a visibleregion upon reaction with ozone gas, said light-detecting unit comprisesa light-receiving surface arranged to face said light-emitting unit,receives, via said sensing element, light emitted by said light-emittingunit, and outputs a signal corresponding to a light quantity received bythe light-receiving surface, and said signal processing unit calculatesan ozone gas amount on the basis of the signal output from saidlight-detecting unit and a light absorption characteristic, obtained inadvance, of said sensing element which contains the dye before reactionwith the ozone gas.
 2. An apparatus according to claim 1, wherein atleast some pores in the porous material are coupled to pores on asurface of the porous material.
 3. An apparatus according to claim 1,wherein a pore in the porous material has such a pore diameter as toattain a predetermined transmittance in the visible light region.
 4. Anapparatus according to claim 3, wherein the pore diameter is not morethan 20 nm at which the dye can enter the pore.
 5. An apparatusaccording to claim 1, wherein the dye comprises an aromatic compoundhaving a diazo group.
 6. An apparatus according to claim 5, wherein thearomatic compound comprises one material selected from the groupconsisting of benzene, naphthalene, and anthracene.
 7. An apparatusaccording to claim 5, wherein the dye comprises a compound having anyone of a hydroxyl group, a sulfurous acid group, and primary to tertiaryamino groups.
 8. An apparatus according to claim 1, wherein the dyecomprises a triphenylmethane stain.
 9. An apparatus according to claim1, wherein the dye contains fuchsonimine.
 10. An apparatus according toclaim 1, wherein the dye contains indigo.
 11. An apparatus according toany one of claims 8 and 9, wherein said sensing element furthercomprises a material having an alkali characteristic in addition to thedye.
 12. An apparatus according to claim 1, wherein said sensing elementfurther comprises an acid gas sorbent in addition to the dye.
 13. Anapparatus according to claim 12, wherein the acid gas sorbent comprisesone material selected from the group consisting of glycerol andtriethanolamine.
 14. An apparatus according to any one of claims 5 and10, wherein said sensing element further comprises an acid in additionto the dye.
 15. An apparatus according to claim 14, wherein the acidcomprises one acid selected from the group consisting of hydrochloricacid, acetic acid, sulfuric acid, and phosphoric acid.
 16. An apparatusaccording to claim 14, wherein said sensing element further comprises ahygroscopic compound in addition to the dye and the acid.
 17. Anapparatus according to claim 16, wherein the hygroscopic compoundcomprises one material selected from the group consisting of glyceroland ethylene glycol.
 18. An apparatus according to any one of claims 5and 10, wherein said sensing element further comprises a buffer inaddition to the dye.
 19. An apparatus according to claim 18, wherein thebuffer comprises phosphoric acid and sodiumdihydrogenphosphatedehydrate.